This invention relates to fluid handling devices, such as medical syringes, in which a plunger is used to deliver fluid from a barrel of the device via a needle.
For safety reasons, e.g. to avoid needle stick injuries, it is desirable that the needle is retracted into the barrel following delivery of the fluid. Our prior U.S. Pat. No. 5,782,804 discloses a fluid handling device provided with a needle retraction mechanism of this type.
The present invention seeks to provide a fluid handling device having a simplified needle retraction mechanism.
According to the present invention there is provided a fluid handling device comprising a barrel for containing fluid to be delivered through a needle, a needlemounting hub at one end of the barrel, a biasing element arranged to urge the hub inwardly of the barrel, a stop element blocking inward movement of the hub into the barrel, a hollow plunger which is movable within the barrel to deliver fluid from the barrel via the needle and has at its forward end a portion which is severable in response to movement of the plunger over the final part of, or at the conclusion of, its delivery stroke to allow retraction of the needlemounting hub into the hollow plunger, the hub and the stop element being formed as plastics mouldings in such a way that the stop element is axially captive with the hub and the plunger being arranged to disengage the stop element and the hub during said final part of, or at the conclusion of, the delivery stroke to allow the biasing element to drive the needle into the hollow plunger.
The stop element may incorporate an integral seal, e.g. a lip seal, which may be annular so as to encircle the stop element.
The stop element and the hub may have interengaged formations at the location of the moulding interface which are caused to separate from one another during said final part of, or at the conclusion of, the delivery stroke of the plunger.
The stop element and the hub may alternatively or additionally be at least partially united. e.g. partially fused, together at the moulding interface, the arrangement being such that the connection is fractured or broken during said final part of, or at the conclusion of, the delivery stroke.
The hub may be elongate and may have a central bore for reception of the needle.
The needle-receiving bore may be of reducing cross-section.
The hub may be produced with some degree of draft, i.e. so as to be of reducing cross section in a direction of travel of the plunger during its delivery stroke.
The biasing element may be a helical spring, usually a compression spring, which may be arranged in encircling relation with the hub. One end of the spring may coact with a forward end of the barrel or an end cap attached to the main body of the barrel and the opposite end of the spring may coact with the hub at a location inwardly of the forward end of the barrel.
The forward end of the plunger may comprise a rim portion and a central blocking portion, the latter forming said severable portion.
The arrangement may be such that, during the final part of or at the conclusion of the plunger delivery stroke, the rim portion of the plunger is arranged to engage the stop element while the hub is arranged to engage the blocking portion, the engagement between the two sets of components being effective to free the hub from the stop element and to free the blocking portion from the rim portion at least to the extent necessary to allow the hub to enter the interior of the plunger.
Preferably the hub is freed from the stop element before the blocking portion is at least partially freed from the rim portion; however, if desired the blocking portion may be freed first or alternatively the hub and the blocking portion may be freed substantially. simultaneously.
The arrangement may be such that the hub and stop element are united together by the moulding process to afford a well-defined threshold at which they break away from one another in response to the application of force to the stop element in the course of operating the plunger.
Preferably one of the components (hub and stop element) is produced as a plastics moulding in a mould having moulding surfaces defined, in part, by the other component, i.e. moulding of one component being effected with the other component in situ.
The two portions may be of plastics materials having different chemical compositions and/or characteristics or they may both be of substantially the same or a similar plastics material.
The hub and stop element may be capable of being broken away from each other without deformation of either of the two portions and, to this end, the moulding interface may be shaped so that no deformation of either component occurs when breaking one from the other.
Alternatively, the hub and the stop element may be interlocked with each other so that some deformation of at least one of the parts occurs when effecting the break.
At the moulding interface, an annular surface of one of the components may be have a configuration complementary with an annular surface of the other component.
The annular surfaces may be cylindrical or of other configuration, e.g. conical.
At the moulding interface, the components may intimately contact each other with a degree of fusion bonding consistent with securing fracture preferentially at the interface region during the break.
The assembly of the hub and stop element may include a detent arrangement acting between the components. The detent arrangement may be provided at or in the vicinity of said moulding interface. For example, the hub and the stop element may, by virtue of the mould design, have interengaging formations which lock the components together to prevent separation, and at least one of the formations may be resiliently deformable to allow the disengagement of the formations on application of sufficient loading to the stop element relative to the hub.
Resistance to separation of the two components may additionally or alternatively be afforded by the nature of the interaction between material or materials of the hub and the stop element at the moulding interface. For instance, there may a shrink type fit between the components at the moulding interface obtained by material shrinkage during cooling following the moulding process.
As a further addition or alternative to the detent arrangement and/or shrink type fit mentioned above, resistance to separation may be provided by fusion bonding between the components at the moulding interface. Such fusion bonding may range from relatively weak, e.g. as a result of some degree of diffusion of material from one component across the moulding interface into the other component, through to relatively strong.
Depending on the nature of interaction desired between the hub and the stop element at the moulding interface, the material or materials from which said portions are produced may be selected so as to secure the desired extent of fusion bonding, if any. For example, if negligible fusion bonding is desired, the materials employed will usually differ in chemical and/or physical characteristics and will be such that no significant diffusion of material takes place across the moulding interface as a result of the moulding process. Similarly the materials can be appropriately selected to obtain the desired degree of fusion bonding where there is a requirement to develop a fusion bond at the moulding interface.
In the latter case for example, the hub and the stop element may be composed of the same material so that significant fusion of the material takes place between the two components.
The width of the moulding interface and hence the zone of contact between the two components may be selected with regard to the required effectiveness of the seal and/or with regard to the resistance to separation of the components required at said interface. For instance, a given degree of resistance may be secured by a relatively narrow interface where the components are strongly fusion bonded together whereas a wider interface may be required if resistance is afforded by shrinkage and/or a weak fusion bond.
Irrespective of how the hub and the stop element are coupled together, the arrangement may be such that the resistance to separation of the two parts is greater with respect to forces applied in one direction compared with forces applied in the opposite direction.
Where one part is moulded in advance of the other and the second part is then moulded with the first part in situ, the first part to be moulded may have a higher heat distortion temperature than the second part so that the first part is not deformed during moulding of the second part.
The stop element and the hub may advantageously be formed in a two-shot moulding process in which one component, e.g. the hub, is initially formed and located so that an annular surface thereof forms a boundary surface of the mould cavity in which the other component is produced so that, during formation of the second component, an annular surface of the latter is conformed with the annular surface of the first component.
The manner of coupling together the hub and the stop element as referred to in the preceding paragraphs may also be employed to couple together the rim portion and the blocking portion, e.g. as disclosed in our U.S. patent application Ser. No. 10/149,342, the entire disclosure of which is incorporated herein by this reference.
Other aspects of the invention include a needle-mounting hub assembly produced as a two-shot moulding and comprising a hub and a stop element captive with the hub, and a method of manufacturing such an assembly.